Parallel contact circuit breaker

ABSTRACT

A parallel pole magnetohydraulic circuit breaker ( 10 ), having a single trip element ( 271 ) and a pair of trip mechanisms ( 101, 102 ), achieving an increased current carrying capacity with reduced nuisance trips. The tip mechanisms ( 101, 102 ) are contained within separate housings ( 14, 16 ), with electrical connections ( 30, 40 ) and multipole trip mechanism ( 101, 102 ) communicating through apertures in the common wall ( 14′ ). Preferably, the armature ( 260 ) of the trip element ( 271 ) acts on a single trip mechanism ( 101, 102 ), which multiplies the available force to trigger a trip of the other tip mechanism.

The present application is a 371 of PCT/US99/24468, filed Oct. 20, 1999,which is a continuation of U.S. patent application Ser. No. 09/176,169,filed Oct. 21, 1998, now U.S. Pat. No. 6,034,586, issued Mar. 7, 2000.

FIELD OF THE INVENTION

The present invention relates to the field of circuit breakers, and moreparticularly to multipole circuit breakers in which contact sets areparalleled in order to increase breaker capacity rating.

BACKGROUND OF THE INVENTION

In the field of electrical circuit breakers, it is well known to tie themechanisms of a plurality of electrical poles, or independent circuitpaths, together. In this case, it is often desired to provide a singlecontrol lever and a trip mechanism which operates the electricalcontacts in synchrony. See, U.S. Pat. Nos. 5,565,828; 5,557,082,4,492,941, and 4,347,488, expressly incorporated herein by reference.

A single pole circuit breaker is a device that serves to interruptelectrical current flow in an electrical circuit path, upon theoccurrence of an overcurrent in the circuit path. On the other hand, amultipole circuit breaker is a device which includes two or moreinterconnected, single pole circuit breakers which serve tosubstantially simultaneously interrupt current flow in two or morecircuit paths upon the occurrence of an overcurrent in any one circuitpath.

In a multipole circuit breaker, typically the poles switch independentphases of AC current. Thus, two-pole and three-pole breakers are wellknown. In these systems, each pole is provided with a current sensingelement to generate a trip signal, so that an overload on any phasecircuit is independently sensed. In the event that an overload occurs,all of the phase circuits are tripped simultaneously. A manual controllever is provided which operates the phase circuits synchronously aswell.

Conventional multipole circuit breaker arrangements thus include a triplever mechanism associated with each pole of the multipole circuitbreaker. Each trip lever includes a portion for joining it to adjacenttrip levers. If any pole is tripped open by an overcurrent, the breakermechanism of that pole causes the trip lever to pivot about its mountingaxis. The pivotal motion of one lever causes all the interconnected triplevers to similarly pivot. Each lever may include an arm for strikingthe armature or toggle mechanism of its respective pole, and causingeach pole to be tripped open.

In order to increase the capacity of a circuit breaker system, it hasbeen proposed to parallel a set of contacts, each of which might beinsufficient alone to handle the composite load. Thus, by parallelingtwo single pole circuit breaker elements, a higher capacity circuitbreaker may be achieved. However, the art teaches that, preferably, asingle contact set is provided having a larger surface area and greatercontact force in order to handle a larger load. These largerload-handling capacity devices are typically dimensionally larger thanlower load carrying designs. This is because, in part, many elementswithin a circuit breaker scale in size in relation with current carryingcapacity, including the lugs, trip elements, trip mechanism, contactsand breaker arm.

In designing a trip element or system, the type of load must beconsidered. There are two main classes of trip elements; thermalmagnetic and magnetohydraulic. These differ in a number ofcharacteristics, and typically have different application in the art.

However, where such contact parallelization is employed, the contactratings of the breaker should be derated from the sum of currentcarrying capacity of each of the contact sets. This is because a contactset having a lower impedance than others will “hog” the current, and maythus see a significantly greater proportion of the total current than50%, resulting in overheating, and possible failure. Therefore, the arttypically teaches that a pair of paralleled contact sets are derated, byfor example about 25%, to ensure that each component will operate withinits safe design parameters. Further, the contact resistance of a switchmay change significantly with each closure of the switch. In parallelcontact systems, it is known to employ both unitary thermal magnetic andmultiple parallel-operating trip elements in multipole breakers. Thus,it is possible to design a circuit breaker with a specially designedtrip element that controls an entire breaker system, or to parallel twoentire breaker circuits of a multipole arrangement. In the later case,in order to equalize the current as much as possible between thecircuits, a current equalization bar has been proposed. However, thisdoes not compensate for unequal contact resistance, and nuisancetripping of the circuit breaker results when the unequal division of thecurrent has caused enough current to pass through one of the currentsensing devices to cause it to trip its associated mechanism.

Attempts have been made in thermal-type breakers to parallel the sets ofcontacts of a multipole breaker to achieve increased maximum currentrating. In one case, exemplified by model QO12150 from Square-D Corp., aunitary thermal magnetic trip element was employed as a trip element fora set of two parallel contact sets, with a connecting member to tripboth contact sets at the same time. In this case, the trip dynamics weredefined by the thermal-magnetic trip element, and careful calibration ofthe thermal element was required. This design provided both contact setswithin a common housing. Thus, while the internal parts were common withnon-multipole arrangements, the housing itself was a special multipolebreaker housing. The parallel breaker is housed in a shell that differsfrom single pole housings, with the parallel poles in a common space.

One typical known system is disclosed in U.S. Pat. No. 4,492,941,expressly incorporated herein by reference, provides electromagneticsensing devices that are electrically connected at one of their ends tothe load terminals. The load terminals are electrically connected inparallel with each other. A plurality of electromagnetic sensing devicesare electrically connected at their other ends to each other and areelectrically connected to all of the movable contacts which arethemselves all electrically connected together. The stationary contactsare connected to line terminals that are also electrically connected inparallel with each other. Thus, the electromagnetic sensing devices areconnected in parallel at both of their ends and the contact sets arealso connected in parallel at both of their electrical ends, while theelectromagnetic sensing devices, on the one hand, and the contact sets,on the other hand, are also in series with each other, thus seeking toequally divide the current among all of the electromagnetic sensingdevices, even though the current may not be equally divided among all ofthe relatively movable contacts, because of varying contact resistances.

Another attempt to increase current carrying capability by parallelingcontact sets using magnetohydraulic trip elements employed two paralleltrip elements, each set for a desired derated value corresponding tohalf of the total desired current carrying capacity. For example, two100 Amp breakers were paralleled (using a standard multipole trip bar)to yield a 150 Amp rated breaker, with 175% trip (about 250 Amps)rating, meeting UL 1077. The parallel set of breakers employed twoside-by-side single breaker housings, with slight modifications, andthus did not require new tooling for housings and contact elements.

In this later case, it is difficult to comply with UL 489, whichrequires that the breaker trip at 135% maximum of rated capacity and200% of rated capacity within 2 minutes, and that the breaker be capableof handling the specified loads without damage. For example, if themaximum expected deviation in contact resistance of the contact sets(which changes each time the contact is closed) could cause a currentsplitting ratio of 60%/40%, then in order to ensure reliable trip at135% of total rated capacity, each trip element must be designed to tripat about 120% of rated capacity, which would lead to unreliability andnuisance trips because of insufficient margin.

Notwithstanding the foregoing attempts, it has heretofore beenconsidered difficult to employ magnetohydraulic circuit breakers inparallel contact multipole breakers with relatively low overcurrentthresholds, such as that imposed by UL 489, especially for use in loadenvironments with high peak to average load ratios, because the maximumexpected currents would result in nuisance trips.

A main advantage of parallel contact circuit breakers is that these mayemploy many parts in common with lower current carrying single poledevices. It is thus often economically desirable to increase the currentcarrying capacity of circuit breakers by modifying as little aspossible, existing circuit breakers. Toward this end, it has beenproposed that the amount of current carrying capacity may be almostdoubled by placing two single pole circuit breakers side-by-side (oralmost tripled by using three side-by-side) and connecting the lineterminals together and likewise connecting the load terminals together.

Commercial circuit breaker manufacturers generally manufacture acomplete product line composed of a number of breaker sizes, each onecovering a different (although sometimes overlapping) operating currentrange. Each breaker size typically has required its own component andcase sizes. In general, each component and case size combination isuseful in circuits having only a single current rating range. The needto have a different set of component and case sizes for each currentrating has added to the overall cost of breakers of this general type.

As discussed above, there are two common types of trip elements forcircuit breakers. A first type, called a thermal magnetic breaker,provides a thermal portion having a bimetallic element that responds toa heat generated by a current, as well as a solenoid to detect magneticfield due to current flow. Typically, the thermal element is designed totrigger a trip response at a maximum of 135% average of rated capacity,and the magnetic element responds quickly (within milliseconds) at 200%of rated capacity. The thermal portion of the breaker controls averagecurrent carrying capability, by means of thermal inertia, while themagnetic element controls dynamic response. This design seeks to provideadequate sensitivity while limiting nuisance trips. However, suchthermal magnetic designs typically require calibration of the thermaltrip mechanism for precision, and tuning of dynamic response isdifficult. Further, the thermal element incurs a wattage loss. Theoperation of the thermal element is also sensitive to ambienttemperature, since the heating of the bimetallic element by the currentflow is relative to the ambient temperature. See, U.S. Pat. Nos.3,943,316, 3,943,472, 3,943,473, 3,944,953, 3,946,346, 4,612,430,4,618,751, 5,223,681, and 5,444,424.

A second type of trip element is called a magnetohydrodynamic ormagnetohydraulic breaker. See, U.S. Pat. Nos. 4,062,052 and 5,343,178.In this element, the current passes through a solenoid coil wound arounda plastic bobbin, acting on static pole piece and a movable armature.Within the solenoid coil is a moveable magnetically permeable core,which is held away from the pole piece in a damping fluid, e.g., aviscous oil, by a spring. As a static current through the coilincreases, the core is drawn toward the pole piece through the viscousfluid, resulting in a nonlinear increase in force on the armature, whichlies beyond the pole piece, as the moveable core nears contact with thepole piece. Thus, as the moveable core is pulled toward the pole piece,the magnetic force on the armature suddenly increases and the armaturerapidly moves. In this case, it is primarily the spring constant of thespring which controls the precision of the trip element, and thus afinal calibration is often unnecessary given the ease of obtainingprecision springs. In the event of a dynamic current surge, the core isdamped by the fluid, and thus does not rapidly move toward the polepiece, resulting in a dynamic overload capability, determined by theviscosity of the damping fluid, and thus avoiding nuisance trips. Thearmature is typically counterbalanced and may be intentionally providedwith an inertial mass to provide further resistance to nuisance trips.

Nuisance tripping is a problem in applications where current surges arepart of the normal operation of a load, such as during motor start-up orthe like. For example, starting up of motors, particularly single phase,AC induction types, may result in high current surges. Motor startingin-rush pulses are usually less than six times the steady state motorcurrent and may typically last about one second, but may be 10 or moretimes the steady state current. In the later case, a breaker may revertto an instantaneous trip characteristic, because the magnetic fluxacting on the armature is high enough to trip the breaker without anymovement of the delay tube core or heating of the thermal element,depending on the design. One way to address this problem is byincreasing the distance between the coil and armature.

A second type of short duration, high current surge, commonly referredto as a pulse, is encountered in circuits containing transformers,capacitors, and tungsten lamp loads. These surges may exceed the steadystate current by ten to thirty times, and usually last for between twoto eight milliseconds. Surges of this type will cause nuisance trippingin conventional delay tube type electromagnetic circuit breakers. Thisproblem may be addressed by increasing the inertia of the trip elementor by other means. See, U.S. Pat. Nos. 4,117,285, 3,959,755, 3,517,357,and 3,497,838, expressly incorporated herein by reference.

SUMMARY AND OBJECTS OF THE INVENTION

The applicants have found that a single magnetohydraulic trip elementcan advantageously be used to provide desired trip dynamics in a circuitbreaker by passing all current from a set of parallel contact setsthrough a unitary trip element, and providing a multipole trip armtriggered by the unitary trip element which trips the parallel contactsets simultaneously.

The preferred design employs parallel circuit breaker poles each havinga trip mechanism, switch contacts and a housing, which share mostcomponents in common with a single pole circuit breaker in the same“family”, thus reducing required number of inventoried parts andengineering costs. The trip element of the preferred design, however,differs from single pole designs, being configured for the desiredratings and dynamic response, and portions of the housing betweenadjacent poles are modified for common access to electrical terminals tobridge the load and to provide a standard type multipole trip bar. Themagnetohydraulic trip element, which is preferably a 150 Amp elementwith desired dynamic trip characteristics, sits asymmetrically in one ofthe pole housings within a standard frame, in the normal trip elementposition, and actuating a standard armature.

The external lugs of each poles are made electrically parallel byplacing a conductive bar therebetween. This also serves the visualfunction of alerting the installer as to the electrical function of thebreaker, which is similar to a multipole breaker that is not paralleled.Internally, one set of lugs are connected together with conductivestraps to one end of the magnetic coil. The other end of the magneticcoil is connected with conductive straps to each of the contact arms. Inorder to provide physical access for these connections, a portion ofeach of the common walls of the breaker pole housings are machined toform an aperture or portal therebetween.

The modifications to the standard single pole housing are minimized;other than the portal in the common wall between the poles, the onlyother modifications are, for example, an arcuate slot for a common tripmechanism, and an arcuate slot for an internal linkage of the manualswitch handles. In the preferred embodiment, however, the handles arelinked externally by a crossbar, which fits between the handles andcauses them to move in unison. In this way, the standard mountings forthe handle, pivot axis of the moveable contact bar, stationary contact,and arc chute and slot motor are unaffected. Further, the safety factorsof the design remain relatively intact.

A preferred design provides two parallel switch poles with a designrating of 100 Amps each, in a housing 2.5 inches long, 0.75 inches wide,and 2 inches deep, with electrical contact bolts on 2 inch centers. Theresulting parallel multipole design with a rating of 150 Amps thereforefits within a form factor of 2.5 by 1.5 by 2 inches, a substantialimprovement over prior 150 Amp rating circuit breakers.

It should be seen that the form factor may be varied according to thepresent invention, for example other standard size circuit breakerswhich may be formed as multipole parallel contact breakers are, forexample, 2 inches long, by 0.75 inches wide, by 1.75 inches deep (e.g.,50 Amp rating) and 7.25 inches long by 1.5 inches wide by 3 inches deep(e.g., 250 Amp rating).

The present invention may incorporate other known circuit breakerfeatures, such as a mid-trip stop for the manual control lever or othertrip indicators, and indeed may be formed into a traditional multipoledesign with parallel sets of contacts for each of multiple switch poles.

It is also seen that, while the preferred embodiments employ housingparts which are common in essential design with single pole designs,that this is not a limitation on the operability of the inventivedesign.

It is therefore an object of the invention to provide amagnetohydrodynamic circuit breaker which has a low average overcurrenttrip capability with good nuisance trip immunity.

It is also an object of the present invention to provide a circuitbreaker having a high current rating and a small form factor.

It is a further object of the invention to provide a circuit breakerhaving a set of parallel contacts, driven by a trip mechanism, whereinall of the contact sets are tripped by a common magnetohydrodynamic tripelement.

These and other objects will be apparent from an understanding of thepreferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

These and further objects and advantages of the invention will be moreapparent upon reference to the following specification, claims andappended drawings wherein:

FIG. 1 is a side view of a single pole breaker mechanism having ahousing half removed;

FIGS. 2A and 2B are detail views of a known breaker toggle mechanism;

FIG. 3A is an exploded view of a parallel pole master/slave circuitbreaker of a slightly different base design than FIG. 1. FIG. 3B shows acutaway view of a delay tube shown in FIG. 3A;

FIGS. 4A and 4B shown, respectively, an exploded view of a housingstructure, and a side view of an inner case half, for the master/slavecircuit breaker according to FIG. 3A.

FIG. 4C shows a partial assembly drawing of exploded view 4A, with a gapbetween the master housing and slave housing, revealing the electricaland mechanical connections between interconnecting the respectivehousings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments will no be described by way of example, inwhich like reference numerals indicate like elements.

EXAMPLE

Components of a conventional type single pole circuit breaker aredepicted in FIGS. 1, 2A and 2B. See, U.S. Pat. No. 5,293,016, expresslyincorporated herein by reference. As shown, the single pole circuitbreaker 10 includes an electrically insulating casing 20 which houses,among other things, stationary mounted terminals 30 and 40. In use,these terminals are electrically connected to the ends of the electricalcircuit that is to be protected against overcurrents.

As its major internal components, a circuit breaker includes a fixedelectrical contact, a movable electrical contact, an electrical arcchute, a slot motor, and an operating mechanism. The arc chute is usedto divide a single electrical arc formed between separating electricalcontacts upon a fault condition into a series of electrical arcs,increasing the total arc voltage and resulting in a limiting of themagnitude of the fault current. See, e.g., U.S. Pat. No. 5,463,199,expressly incorporated herein by reference. The slot motor, consistingeither of a series of generally U-shaped steel laminations encased inelectrical insulation or of a generally U-shaped, electricallyinsulated, solid steel bar, is disposed about the contacts toconcentrate the magnetic field generated upon a high level short circuitor fault current condition, thereby greatly increasing the magneticrepulsion forces between the separating electrical contacts to rapidlyaccelerate separation, which results in a relatively high arc resistanceto limit the magnitude of the fault current. See, e.g., U.S. Pat. No.3,815,059, incorporated herein by reference.

The trip mechanism includes a contact bar, carrying a movable contact ofthe circuit breaker, which is spring loaded by a multi-coil torsionspring to provide a force repelling the fixed contact. In the closedposition, a hinged linkage between the manual control toggle is held inan extended position and provides a force significantly greater than thecountering spring force, to apply a contact pressure between themoveable contact and the fixed contact. The hinged linkage includes atrigger element which, when displaced against a small spring andfrictional force, causes the hinged linkage to rapidly collapse,allowing the torsion spring to open the contacts by quickly displacingthe moveable contact away from the fixed contact. The trigger element islinked to the trip element.

As is known, the casing 20 also houses a stationary electrical contact50 mounted on the terminal 40 and an electrical contact 60 mounted on acontact bar 70. Significantly, the contact bar 70 is pivotally connectedvia a pivot pin 80 to a stationary mounted frame 100. A helical spring85, which encircles the pivot pin 80, pivotally biases the contact bar70 toward the frame 100 in the counterclockwise direction per FIG. 1. Acontact bar stop pin 90 or contact bar stop mounted on the contact bar70 (or optionally other stop, such as a surface which contacts theframe), limits the pivotal motion of the contact bar 70 relative to theframe 100 in the non-contacting position (contact bar 70 rotated aboutpin 80 in the counterclockwise direction to separate contacts 50 and 60,not shown in FIG. 1). By virtue of the pivotal motion of the contact bar70, the contact 60 is readily moved into and out of electrical contactwith the stationary contact 50. In the contacting position (shown inFIG. 1), the stationary contact 50 limits the motion of the contact 60,thus limiting the angular rotation of the contact bar 70 about pin 80.The pivot pin 80 sits in a conforming aperture in the frame, while aslot 81 is provided in the contact bar 70 to allow a small amount ofvertical displacement. Thus, in the contacting position, the contact bar70 may be displaced vertically by the pressure of the toggle linkagecomposed of cam link 190 and link housing 200 in the aligned relativeorientation (shown in FIG. 1), against a force exerted by the helicalspring 85.

An electrical coil 110, which encircles a magnetic core 120 topped by apole piece 130, is positioned adjacent the frame 100. An extension 140of the coil material, typically a solid copper wire, or an electricalbraid, serves to electrically connect the terminal 30 to one end of thecoil 110. An electrical braid 150 connects the opposite end of the coil110 to the contact bar 70. Thus, when the contact bar 70 is pivoted inthe clockwise direction (as viewed in FIG. 1), against the biasing forceexerted by the spring 85, to bring the contact 60 into electricalcontact with the contact 50, a continuous electrical path extendsbetween the terminals 30 and 40.

Magnetic core 120 includes a delay tube. By way of example only, thecoil and delay tube assembly may be of the type shown and described inU.S. Pat. No. 4,062,052, expressly incorporated herein by reference.

Magnetic core 120 has at an upper position thereof, a pole piece 130.Adjacent pole piece 130 is an armature 260 pivotally mounted on a pin261 secured to frame 100. Armature 260 is rotatably biased in aclockwise direction (relative to FIG. 3) by a spring (not shown), andcomprises an arm 265 and a counterweight 266. Counterweight 266comprises an enlarged extension of armature 260, and may include a slot267 for receiving a pin of an inertia wheel rotatably mounted on frame100, not shown. See, U.S. Pat. Nos. 3,497,838, 3,959,755, 4,062,052, and4,117,285, expressly incorporated herein by reference.

The delay tube of the magnetic core 120 is a typical design, which isdisclosed, for example, in U.S. Pat. No. 4,062,052, expresslyincorporated herein by reference. In this design, an outer tube 122 ofthe magnetic core 120 is supported in the frame 100 by a bobbin 121,about which the coil 110 is wound. The outer tube is a drawn singlepiece shell, sealed at its open end by the pole piece 130. The interiorof the delay tube is conventionally filled with a viscous fluid 123 suchas oil. Typically, the viscosity of the oil is selected to provide adesired damping within a standard delay tube design, although mechanicalmodifications, most notably with respect to the clearance around amagnetic delay core 124 (not shown in FIG. 1) or slug in the outer tube122, will also influence the damping or delay of the system. Theconstruction materials of the magnetic delay core or slug and pole piece130 may also alter the force induced by the coil 110. The delay core orslug is biased away from the pole piece 130 by a helical spring 125provided within the outer shell 122. For example, the delay core has anenlarged lower end and a reduced diameter upper end around which aportion of spring passes and defining an annular shoulder against whichthe lower end of spring bears. In conventional circuit breaker delaytubes, the distance from the bottom of the core to the plane containingthe bottom of the coil 110, is customarily chosen to be about one-thirdof the overall interior distance of the delay tube, namely from thebottom of the core to the underside of the pole piece 130. Customarily,the coil 110 surrounds the upper two-thirds of the delay tube outershell 122. This conventional construction optimizes the delay functionof the tube while, at the same time, maintaining the overall length ofthe tube within reasonable bounds.

When a prolonged overcurrent passes through coil 110, delay core movesupwardly in the outer shell 122, with motion damped by the viscous oil,to compress spring until the upper end of delay core engages pole piece130, causing an increased magnetic flux in the gap between the polepiece 130 and armature 260, so that the armature 260 is attracted to thepole piece 130 and rotates about its pivot 261 to engage the searstriker bar 240 to result in collapse of the toggle mechanism,separating the electrical contacts and opening the circuit in responseto the overcurrent, as will become apparent below.

The circuit breaker 10 also includes a handle 160, which is pivotallyconnected to the frame 100 via a pin 170. Handle 160 includes a pair ofears 162 with apertures for receiving a pin 180, which connects handle160 to a cam link 190. In addition, a toggle mechanism is provided,which connects the handle 160 to the contact bar 70. The handle 160 isprovided with a helical spring 161, which applies a counterclockwiseforce on the handle 160 about pin 170 with respect to frame 100. Asignificant feature of the cam link 190, shown in expanded view in FIG.2B, is the presence of a step, formed by the intersection ofnon-parallel surfaces 194 and 198, in the outer profile of the cam link190. Cam link 190 is pivotally connected by a rivet or pin 210 to ahousing link 200.

With further reference to FIGS. 2A and 2B, the toggle mechanism of thecircuit breaker 10 also includes a link housing 200, which is furtherconnected a projecting arm 205. The link housing is pivotally connectedto the cam link 190 by a pin or rivet 210 and pivotally connected to thecontact bar 70 by a rivet 220.

The toggle mechanism further includes a sear assembly, including a searpin 230 which extends through an aperture in the link housing 200generally corresponding to a location of an outer edge 195 of the camlink 190. This sear pin 230 includes a circularly curved surface 232(see FIG. 2B) which is intersected by a substantially planar surface233. The sear assembly also includes a leg 235 (see FIG. 2A), connectedto the sear pin 230, and a sear striker bar 240, which is connected tothe leg 235 and projects into the plane of the paper, as viewed in FIG.2A. A helical spring 250, which encircles the sear pin 230, pivotallybiases the leg 235 of the sear assembly clockwise, into contact with theleg 205 of the link housing 200, and biasing the planar surface 233 ofthe sear pin 230 into substantial contact with the bottom surface 198 ofthe step in the cam link 190. A force exerted against the sear strikerbar 240 is transmitted to the leg 235, and acts as a torque on the searpin 230 to angularly displace the substantially planar surface 233 ofthe sear pin 230 from coplanarity the surface 198 of the cam link 190,thus raising the leading edge 234 of the substantially planar surface233 of the sear pin 230 above the top edge of the surface 194. Thisrotation results in elimination of a holding force for the contact bar70 in the contacting position, generated by the helical spring 85 actingon the contact arm 70, through the rivet 220 and link housing 200 andsear pin 230 leading edge 234, against the surface 194 of the cam link190, acting on the pin 180, ears 162 of handle 160, held in place by pin170 with respect to the casing 20 and frame 100.

The initial clockwise rotation of the cam link 190 is limited by a hook199 in the outer profile of the cam link 190, at a distance from thestep, which partially encircles, and is capable of frictionallyengaging, the sear pin 230. In addition, the distance from the step tothe hook 199 is slightly larger than the cross-sectional dimension,e.g., the diameter, of the sear pin 230. This dimensional differencedetermines the amount of clockwise rotation the cam link 190 undergoesbefore this rotation is stopped by frictional engagement between thehook 199 and the sear pin 230.

As a consequence, the sear pin 230 engages the step in the cam link 190,i.e., a portion of the surface 194 of the cam link 190 overlaps andcontacts a leading portion of the curved surface 232 of the sear pin230. Thus, it is by virtue of this engagement that the toggle mechanismis locked and thus capable of opposing and counteracting the pivotalbiasing force exerted by the spring 85 on the contact bar 70, therebymaintaining the electrical connection between the contacts 50 and 60.

By manually pivoting the handle 160 in the counterclockwise direction(as viewed in FIG. 1), the toggle mechanism, while remaining locked, istranslated and rotated out of alignment with the pivotal biasing forceexerted by the spring 85 on the contact bar 70. This biasing force thenpivots the contact bar 70 in the counterclockwise direction, toward theframe 100, resulting in the electrical connection between the contacts50 and 60 being broken, thus assuming a noncontacting position. When inthe full counterclockwise position, the handle 160 applies a slighttension or no force on the cam link 190, resulting in a full extensionof the cam link 190 with respect to the link housing 200. In thisposition, the leading edge of the surface 232 of the sear pin 230engages the surface 194, and thus the toggle mechanism is in its lockedposition. Therefore, manually pivoting the handle 160 from the left toright, i.e., in the clockwise direction, then serves to reverse theprocess to close the contacts 50, 60, since a force against the actionof spring 85 is transmitted by clockwise rotation of the handle to thecontact bar 70.

As shown in FIG. 1, the armature 260, pivotally connected to the frame100, includes a leg 265 which is positioned adjacent the sear strikerbar 240. In the event of an overcurrent in the circuit to be protected,this overcurrent will necessarily also flow through the coil 110,producing a magnetic force which induces the armature 260 to pivottoward the pole piece 130. As a consequence, the armature leg 265 willstrike the sear striker bar 240, pivoting the sear pin 230 out ofengagement with the step (intersection of surfaces 194, 198) in the camlink 190, thereby allowing the force of spring 85 to collapse the togglemechanism. In the absence of the opposing force exerted by the togglemechanism, the biasing force exerted by the spring 85 on the contact bar70 will pivot the contact bar 70 in the counterclockwise direction,toward the frame 100, resulting in the electrical connection between thecontacts 50 and 60 being broken.

As a safety precaution, the operating mechanism is configured to retaina manually engageable operating handle 160 in its ON or an intermediate,tripped position, if the electrical contacts 50, 60 are welded together.Thus, the handle 160 will not assume the OFF position if the contactsare held together. In addition, if the manually engageable operatinghandle 160 is physically restricted or obstructed in its ON position,the operating mechanism is configured to enable the electrical contacts50, 60 to separate upon a trip, e.g., due to an overload condition orupon a short circuit or fault current condition. See, U.S. Pat. No.4,528,531, expressly incorporated herein by reference.

Two or more single pole circuit breakers 10 are readily interconnectedto form a multipole circuit breaker. In this configuration, each suchsingle pole circuit breaker 10 further includes, as depicted in FIG. 1,a trip lever 270 (shown in dotted line) which is pivotally connected tothe frame 100 by pin 261, which also is the pin about which the armature260 pivots. The trip lever 270 is generally U-shaped and includes arms280 (shown in FIG. 1) and 290 (not shown in FIG. 1) which at leastpartially enfold the frame 100. A helical spring 330, positioned betweenthe frame 100 and the arm 280 and encircling the pin 162, pivotallybiases the trip lever toward the frame 100. A projection 300 of the triplever 270, which, as viewed in FIG. 1, projects out of the plane of thepaper, is intended for insertion into a corresponding aperture 301 inthe trip lever of an adjacent single pole circuit breaker. Thus, anypivotal motion imparted to the trip lever 270, in opposition to thebiasing force exerted by the spring 330, is transmitted to the adjacenttrip lever, and vice versa. The projection 300 and aperture of a triplever of an adjacent breaker, are preferably tapered, to ensure a securefit therebetween. When the toggle link collapses, a protrusion 291 (notshown in FIG. 1) from the contact bar 70 displaces a cam surface 292 ofthe arm 290, thus rotating the trip lever about pin 261, and displacingthe projection 300. The projection 300 thus moves in an arc about thepin 261, and thus an arcuate slot is provided in a housing half ofhousing 20 to transmit forces through the projection 300. A portion ofarm 280 acts directly on the sear striker bar 240, to trip theassociated toggle mechanism of an adjacent switch pole. A protrusionfrom the frame, for example a stop, limits the motion of arm 290 of thetrip lever 270, in response to a bias spring about the pivot axis. Thus,Since the trip lever 270 is not operated directly by the armature 260,the trip dynamics of the circuit breaker are unaffected. The drag on thetrip mechanism from the trip lever 270 is insignificant.

Side 280 has a cam surface 285, having a bend of about 45 degrees, whichengages the sear striker bar 240 at about the position of the bend. Side290 has a bend 293, forming cam surface 292, which is perpendicular withthe portion of the side 290. Protrusion 291 extends from the side of themoveable contact bar 70, which contacts the surface 292 midway throughthe travel of the contact bar 70. When the contact bar 70 is displaced,the protrusion 291 pushes against the surface 292, causing a rotationabout the pin 261, causing the surface 285 of side 280 to displace thesear striker bar 240. It is clear that in operation, rotation of triplever 270 about pin 261 will result in tripping of the toggle mechanism,and tripping of the toggle mechanism will result in rotation of the triplever about the pin 261. See, e.g., U.S. Pat. Nos. 5,557,082, 5,214,402,5,162,765, 5,117,208, 5,066,935, and 4,912,441, and also U.S. Pat. Nos.4,492,941, 4,437,488, 4,276,526, and 3,786,380, expressly incorporatedherein by reference.

In addition to the above-described “master” pole, adjacent thereto isprovided a “slave” pole. This “slave” pole is identical to the “master”pole with the exception that it lacks the coil 110, magnetic core 120,pole piece 130, and armature 260. The projection 300 passes throughaligned arcuate slots in the respective case walls between the adjacent“master” and “slave” switch pole housings 20. The trip lever 271 in the“slave” pole, like the trip lever 270 of the “master” pole, receives atorque with respect to its frame from the tapered projection 300,extending laterally from the “master” pole housing 20 into the “slave”pole housing 20, into a tapered recess of the trip lever 271 of the“slave” pole. As the trip lever 271 in the “slave” pole rotates, itapplies a force to the “slave” pole sear striker bar 240, which in turnrotates the “slave” pole sear pin 230 about its axis, resulting incollapse of the “slave” pole toggle mechanism 102. Thus, when the“master” mechanism 101 trips or is manually switched OFF, the “slave”mechanism 102 trips slightly thereafter. A dual ended rod 302 connectsthe handle 160 of the master and slave circuit breakers so that theymove in unison.

As shown in FIG. 3, an electrical braided wire 141 serves to connect theterminal 30 in the “master” pole and an electrical braid 142 serves toelectrically connect the terminal 31 in the “slave” pole to one end ofthe coil 110. Electrical braids 150, 152 connect the opposite end of thecoil 110 to the contact bars 70, 71 of the “master” and “slave” poles,respectively. Electrical braid 151 passes through a rectangular portalformed in both adjacent case halves. The end of the coil 110 extendsthrough the portal, so that electrical braid 142 does not have to passthrough the portal, and indeed, to facilitate connection, the braid 141may partially or completely pass through the portal to join the end ofcoil 110. Conductive plates 43, 42 are provided for bridging the lugconnections 30, 31 and 40, 41, respectively, to ensure low impedancebetween the “master” and “slave” mechanisms.

To extinguish arcing caused by opening of the contacts 50 and 60, astacked array of metal plates 73 (shown in FIG. 3) are supported withinand by the two half cases 14 and 16 of the circuit breaker housing 20around the moveable contact arm 70.

Each housing casing half 14, 16 includes the following features: Anupper boss (half) for the toggle handle 21; a lower access port 22; aset of four rivet holes for assembly 23; a pair of half-recesses for amounting nut 24; a first pivot recess for the handle pin 25; a secondpivot recess for the contact arm pin 26; a pair of half-recesses forelectrical contact lugs 27; a set of indentations for supporting the arcchute members 28; and a number of side port halves 29. In addition, eachrespective inner case half 16, 14′ of the “master” and “slave” housing,respectively, has a number of apertures. First, a generally rectangularportal 31 is provided for paralleling the electrical connections fromthe pair of lug contacts 30, 31 and the movable contact bars 70, 71.Second, an arcuate aperture 32 is provided for the projection 300 of thetrip lever 270. Optionally, an arcuate slot 33 is provided for aninternal pin connecting the manual operation handles, causing them tooperate synchronously. A cover 34 is provided to close each of the loweraccess ports. Each of the “master” and “slave” housings 20 are about 2.5inches long, 0.75 inches wide, and 2 inches deep, with electricalcontact bolts on 2 inch centers, each being individually rated at about100 Amps. The resulting parallel multipole design with a rating of 150Amps therefore fits within a form factor of 2.5 by 1.5 by 2 inches,

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are, therefore, to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are, therefore, intended to be embracedtherein. The term “comprising”, as used herein, shall be interpreted asincluding, but not limited to inclusion of other elements notinconsistent with the structures and/or functions of the other elementsrecited.

What is claimed is:
 1. A circuit breaker, comprising: (a) a commonmagnetohydrodynamic load sensor; and (b) at least two sets ofinterruptable electrical contacts, each having an associated tripmechanism and a rated load capacity, wherein said magnetohydrodynamicload sensor responds to a sensed load by tripping at least one set ofinterruptable electrical contacts, and is adapted to sense a loadexceeding said rated capacity of a single set of interruptableelectrical contacts and within a composite load capacity of said atleast two sets of interruptable electrical contacts in parallel.
 2. Thecircuit breaker according to claim 1 wherein said magnetohydrodynamicload sensor comprises an inductive coil having first and second ends,said inductive coil surrounding a magnetically permeable core, saidmagnetically permeable core being displaceable against a spring force inresponse to a current flowing through said inductive coil, a movement ofsaid magnetically permeable core being damped by a viscous fluid, and anarmature, disposed proximate to an end of said inductive coil such thata current in said inductive coil induces a magnetic field which acts toattract said armature, wherein the magnetohydrodynamic load sensor tripssaid trip mechanism of a set of interruptable electrical contacts when asufficient magnetic force is generated to displace said armature.
 3. Thecircuit breaker according to claim 1 wherein each set of interruptableelectrical contacts comprises a fixed contact and a displaceable contactdisposed on a spring loaded pivoting contact arm, and wherein said tripmechanism comprises a collapsible toggle link mechanism.
 4. The circuitbreaker according to claim 1, wherein each of said sets of interruptableelectrical contacts is connected on one side to said commonmagnetohydrodynamic load sensor and splitting an electrical currentpassing therethrough.
 5. The circuit breaker according to claim 1,wherein each of the sets of interruptable electrical contacts iselectrically parallel.
 6. The circuit breaker according to claim 1,wherein said common magnetohydrodynamic load sensor trips a first set ofinterruptable electrical contacts, and a trip of said first set ofinterruptable electrical contacts trips a second set of interruptableelectrical contacts.
 7. The circuit breaker according to claim 1,wherein said circuit breaker has a rated load capacity of about 150Amps.
 8. The circuit breaker according to claim 1, wherein said circuitbreaker has a rated load capacity of about 150 Amps, comprising two setsof interruptable electrical contacts, each having a rated load capacityof about 100 Amps, said circuit breaker fitting in a housing about 2.5inches long, 1.5 inches wide, and 2 inches deep.
 9. The circuit breakeraccording to claim 1, wherein respective sets of interruptableelectrical contacts are disposed in separate respective stacked housingcompartments, each having at least one inner wall, each respective innerwall having at least one aperture formed therein.
 10. The circuitbreaker according to claim 9, wherein said trip mechanism of a first setof interruptable electrical contacts is interconnected with a tripmechanism of a second set of interruptable electrical contacts throughsaid aperture.
 11. The circuit breaker according to claim 10, wherein asensing of an overload condition by said magnetohydrodynamic load sensorinitiates a trip of a first set of interruptable electrical contactsthrough its associated trip mechanism, and said associated tripmechanism of said first set of interruptable electrical contactsinitiates a trip of a second set of interruptable electrical contactsthrough its associated trip mechanism, to provide simultaneous trippingof said first and second sets of interruptable electrical contacts. 12.A circuit breaker, comprising: (a) a master breaker, having within afirst sub-housing a common magnetohydrodynamic load sensor having a tripload and a first set of interruptable electrical contacts, having afirst trip mechanism and a first rated load capacity, wherein said tripload exceeds said first load capacity; and (b) a slave breaker, havingwithin a second sub-housing a second set of interruptable electricalcontacts, having a second trip mechanism and a second rated loadcapacity, wherein said magnetohydrodynamic load sensor responds to aload exceeding said trip load by tripping said first trip mechanism; atrip of said first set of interruptable electrical contacts results in atripping of said second set of interruptable electrical contacts; and acomposite load capacity of said first set of interruptable electricalcontacts and said second set of interruptable electrical contactsexceeds said trip load.
 13. The circuit breaker according to claim 12,wherein an aperture is formed in adjacent walls of said first and secondsub-housings to provide a mechanical signal from said first sub-housingto said second sub-housing indicating that said load exceeds said tripload.
 14. A method for providing a high load capacity circuit breakerhaving a desired load capacity, comprising the steps of: (a) providing amagnetodynamic load sensor at the desired load capacity; (b) providingat least two set of electrical switch elements, each having a loadcapacity insufficient to meet the desired load capacity, but which inparallel meet the desired load capacity; (c) wiring the sets ofelectrical switch elements in parallel; (d) when the load exceeds thedesired load capacity, causing an interrupter of the first of theelectrical switch elements to trip and thereby to cease conducting; and(e) sensing a trip of the first of the electrical switch elements tocause an interrupter of a second of the electrical switch elements totrip and thereby to cease conducting, to thereby block current to theload.
 15. The method according to claim 14, wherein each set ofelectrical switch elements is provided in a separate sub-housing, andwherein the magnetodynamic load sensor is situated primarily in a singleone of said sub-housings.
 16. The method according to claim 14, whereineach set of electrical switch elements comprises a fixed contact and adisplaceable contact disposed on a spring loaded pivoting contact arm,and wherein the interrupter comprises a collapsible toggle linkmechanism.
 17. The method according to claim 14, wherein themagnetodynamic load sensor comprises an inductive coil having first andsecond ends, the inductive coil surrounding a magnetically permeablecore, the magnetically permeable core being displaceable against aspring force in response to a current flowing through the inductivecoil, a movement of the magnetically permeable core being damped by aviscous fluid, and an armature, disposed proximate to an end of theinductive coil such that a current in the inductive coil induces amagnetic field which acts to attract the armature, wherein themagnetodynamic load sensor trips the interrupter of a set of electricalswitch elements when a sufficient magnetic force is generated todisplace the armature.